Hydration of n-Butenes (sec-Butanol [CH₃CHOHCH₂CH₃])

sec-Butanol (2-butanol, sec-butyl alcohol), a liquid, has a strong characteristic odor. Its normal boiling point is 99.5°C, which is near water’s. The alcohol is soluble in water but less so than isopropyl and ethyl alcohols. sec-Butanol is produced by a reaction of sulfuric acid with a mixture of n-butenes followed by hydrolysis. Both 1-butene and cis- and trans-2- butenes yield the same carbocation intermediate, which further reacts with the HSO₄^- or SO₄^2- ions, producing a sulfate mixture:

The sulfation reaction occurs in the liquid phase at approximately 35°C. An 85 wt% alcohol yield could be realized. The reaction is similar to the sulfation of ethylene or propylene and results in a mixture of sec-butyl hydrogen sulfate and di-sec-butyl sulfate. The mixture is further hydrolyzed to sec-butanol and sulfuric acid:

The only important by-product is di-sec-butyl ether, which may be recovered. The major use of sec-butanol is to produce MEK by dehydrogenation, as mentioned earlier. 2-Butanol is also used as a solvent, a paint remover, and an intermediate in organic synthesis.